Referring to FIG. 1, the exhaust gas 10 emitted to an exhaust treatment system 12 from an internal combustion engine (not shown) is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter. Catalyst compositions typically disposed on catalyst supports or substrates are provided in various exhaust system devices to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
An exhaust treatment technology, in use for high levels of particulate matter reduction, particularly in diesel engines, is the Particulate Filter (“PF”) device 14. There are several known filter structures used in PF devices that have displayed effectiveness in removing the particulate matter from the exhaust gas 10 such as ceramic honeycomb wall flow filters, wound or packed fiber filters, open cell foams, sintered metal fibers, etc. Ceramic wall flow filters have experienced significant acceptance in automotive applications.
The filter in a PF device 14 is a physical structure for removing particulates from exhaust gas 10 and, as a result, the accumulation of filtered particulates will have the effect of increasing the exhaust system backpressure experienced by the engine. To address backpressure increases caused by the accumulation of exhaust gas particulates, the PF device 14 is periodically cleaned, or regenerated. The regeneration operation burns off the carbon and particulate matter collected in the filter substrate and regenerates the PF device 14.
Regeneration of a PF device 14 in vehicle applications is typically automatic and is controlled by an engine or other controller 15 based on signals generated by engine and exhaust system sensors such as Temperature sensors T1, T2 and back pressure sensors B1. The regeneration event involves increasing the temperature of the PF device 14 to levels that are often above 600 C in order to burn the accumulated particulates.
One method of generating the temperatures required in the exhaust system for regeneration of the PF device 14 is to deliver unburned HC (often in the form of raw fuel) 16 to an oxidation catalyst (“OC”) device 18 disposed upstream of the PF device. The HC 16 may be delivered by injecting fuel (either as a liquid or pre-vaporized) directly into the exhaust gas 10 using an HC injector/vaporizer 20. The HC 16 is oxidized in the OC device 18 resulting in an exothermic reaction that raises the temperature of the exhaust gas 10. The heated exhaust gas travels downstream to the PF device 14 to thereby burn (oxidize) the particulate accumulation. A challenge for designers, especially those involved in space limited automotive engineering, is that injecting fluids such as HC 16 into the exhaust gas 10 upstream of the OC device 18, or any other device for that matter, must allow for sufficient residence time, turbulence and distance in the exhaust flow 10 for the injected fluid to become sufficiently mixed and vaporized prior to entering the device. Without proper preparation, the injected fluid, HC 16 for instance, will not properly oxidize in the OC device 14 and some unburned HC may pass through the device resulting in wasted fuel passing through the exhaust treatment system 12 and local hot and cool spots within devices 14 and 18. Turbulators (Static Mixers) or other mixing devices 22 may be installed in an exhaust conduit 24 that fluidly connects the various exhaust treatment devices to aide in mixing the injected fluid. Such mixing devices, while effective, may add undesirable backpressure to the exhaust treatment system 12, reducing engine performance.
A technology that has been developed to reduce the levels of NOx emissions in lean-burn engines (ex. diesel engines) that burn fuel in excess oxygen includes a selective catalytic reduction (“SCR”) device 28. The SCR catalyst composition disposed in the SCR device preferably contains a zeolite and one or more base metal components such as iron (“Fe”), cobalt (“Co”), copper (“Cu”) or vanadium (“V”) which can operate efficiently to reduce NOx constituents in the exhaust gas 10 in the presence of a reductant (not shown) such as ammonia (‘NH3”). The reductant is typically delivered upstream of the SCR device, in a manner similar to the HC discussed above, and travels downstream to the SCR device 28 to interact with the SCR catalyst composition; reducing the levels of NOx in the exhaust gas passing through the SCR device. Like the HC discussed above, without proper mixing, the injected reductant, urea or ammonia for instance, will not properly function in the SCR device and some of the fluid may pass through the device resulting in wasted reductant as well as reduced NOx conversion efficiency.
With continuing reference to FIG. 1, typical exhaust treatment systems 12 may include several exhaust treatment devices as described above. In many instances, whether historical or not, the devices may comprise individual components that are serially disposed along the exhaust conduit 24 that extends from the exhaust manifold outlet of the internal combustion engine (not shown) to the tailpipe outlet (not shown) of the exhaust treatment system 12. The individual components typically comprise catalyst coated substrates that are encased in ridged canisters 32 constructed of stainless steel, to resist corrosion and extend operational life. The canisters 32 each have an inlet and an outlet at either end to permit the flow of exhaust gas therethrough. The canisters typically have of inlet and outlet cones 34, 36 respectively, placed at either end which are configured to allow the exhaust gas 10 that is entering a device to transition smoothly from a relatively small diameter exhaust conduit 24 into a larger diameter exhaust treatment device which has been sized based on the maximum engine exhaust flow rate and the quantity of exhaust catalyst volume deemed necessary to adequately treat the specific exhaust component (“CO”, “HC”, NOx, etc.). A problem with this configuration is that it is necessary to choose a reasonable length between components, as well as sufficient mixing devices 22 disposed within the exhaust conduit, to achieve adequate mixing of injected fluids (ex. HC and Urea (ammonia) reductant). On the other hand, as vehicle architectures become smaller, the desired length for the exhaust treatment system 12 discussed above is not necessarily available.
Accordingly it is desirable to provide an apparatus that will achieve uniform mixing and distribution of a fluid injected into the exhaust gas 10 in an exhaust treatment system 12 in a compact distance.